A film made of a thermoplastic resin has excellent characteristics, and is used in many industries. As representative films, for example, a polyester film, an aramid-based film, an olefin-based film, a polypropylene film, a PPS (polyphenylene sulfide) film, and a PET (polyethylene terephthalate) film have been known. In addition, a film has been known which is made of a material such as PE (polyethylene), POM (polyoxymethylene or an acetal resin), PEEK (polyetheretherketone), an ABS resin (acrylonitrile, butadiene, a styrene copolymer synthetic resin), PA (polyamide), PFA (tetrafluoroethylene, a perfluoroalkoxyethylene copolymer), PI (polyimide) and PVD (polyvinyl dichloride).
In fields such as smartphones, tablet terminals, liquid crystal displays, solar light panels and automobiles, the application of a highly functionalized film has been expanded as a necessary component. A film is highly functionalized by technologies for not only high functionalization of a film material but also for high functionalization of a film layer structure (bulk control), multilayer lamination of a film and surface control of a film.
In the multilayer lamination of a film and the surface control of a film, for example, a surface modification of a film described in a Patent Document 1 is performed. In general, an object of the surface modification is to improve barrier properties, durability and wettability (adhesive properties), and the surface of the film having hydrophobicity (water repellency) is modified to the surface of the film having hydrophilicity. That is, the molecular structure of the surface of a film material is broken by some means, and by adding an OH group or an O group having hydrophilicity, the surface of the film is modified.
As a specific means for modifying the surface of the film, there are methods such as (1) physical modification methods such as corona discharge, plasma treatment and sputtering treatment, (2) a modification method by ultraviolet light irradiation or electron beam irradiation, (3) a modification method by reactive gases such as ozone, and (4) a wet modification method by chemical liquid or ozone water.
It is considered that the modification method of (2) by ultraviolet light irradiation or electron beam irradiation is not suitable as a method for modifying only the surface of the film, when the film having a property in which these ultraviolet light and the electron beam are transmitted easily is taken into consideration.
In addition, as to the modification method of (3) by the reactive gases, there is a possibility that a sufficient modification effect of the surface of the film cannot be obtained. For example, there is a possibility that oxygen radicals that are a reaction active species and which contribute to modification reaction cannot be sufficiently supplied to the surface of the film, even if ozone gas that is a representative reactive gas is used. The compulsive decomposition of the ozone gas is therefore performed by irradiating ultraviolet light to the ozone gas, to increase the supply amount of the oxygen radicals (see, for example, a Patent Document 2). However, the oxygen radicals generated by the ultraviolet light irradiation are oxygen radicals in an excited state, and reactivity is extremely high, and consequently, control is difficult. That is, in a case where ultraviolet light is irradiated to the ozone gas, the modification effect becomes high, as compared with a case where the surface modification is performed by only the ozone gas. However, it is difficult to supply the oxygen radicals to the surface of the film, and there is a possibility that a sufficient modification effect cannot be obtained.
In addition, as to the wet modification method of (4), there is a possibility that an application field is limited, because a step for drying the film is required after treatment, and a post-treatment and a treatment facility for the chemical liquid used for modification treatment are required.
Due to the above reasons, the physical modification methods of (1) having the highest modification effect have been the most widely used.
However, there is a possibility that fine modification control, such as the uniformity of the modification effect, by the corona discharge and the plasma treatment which are widely used as the physical modification methods of (1) becomes difficult, because electric discharge in the corona discharge and the plasma treatment occurs by dielectric breakdown of the gas between electrodes, and the modification effect is affected by the shape of the electrode and the state of the surface of the electrode. In addition, there is not a few possibility that the temperature of a film as a substrate becomes high by heat generation associated with the discharge, and the film is extremely damaged. Moreover, there a is possibility that a long-term fixed modification effect cannot be obtained because the surface of the electrode deteriorates with time by the discharge
Moreover, in the physical modification methods of (1), there is a possibility that the modification effect is lost with the lapse of time. For example, in a film in which the contact angle of a water drop has been made small by hydrophilic treatment, it has been known that there is a case where the contact angle of the water drop returns to a state close to the state before the treatment in a few days. It is therefore difficult to storage the film for a long period of time, and there is also a case where the hydrophilic treatment is performed twice immediately after producing the film and before using the film to keep the hydrophilicity of the film.